The present invention relates to construction of railway grade crossings where railroads intersect vehicular roads, and in particular to such grade crossings where a portion of the vehicular roadway includes concrete panels that are supported atop the railroad ties of the railroad track.
At railway grade crossings cast concrete xe2x80x9cfillerxe2x80x9d panels or slabs are used to fill the spaces between the rails and along the outer side of each rail to provide a roadway surface. Such concrete panels rest on top of the railroad ties, with each panel covering several ties and having its top surface aligned with the roadway surface to establish a smooth crossing for vehicles. Despite having been engineered to withstand the weight of vehicular traffic, these panels are subject to wear and can fail prematurely.
The concrete filler panels used in grade crossings are typically not loaded other than by their own weight. When a heavy truck passes over the crossing, the panels are subjected to bending stresses, tending to deflect downward where the tires of vehicles pass over areas of the panels that are not directly supported by the ties. If the tops of the ties are not even with each other, a panel might bridge the distance between several ties without actually contacting the tops of intermediate ties. If a panel is flexible enough, under a heavy road-traffic load it might deflect so that the undersurface of the panel is brought into contact with the tops of low-standing intermediate ties. Once the panel touches the top of a low-standing tie, it is then supported by that tie and does not deflect further. In some cases, it is not the bending stress sustained by the entire panel that causes the panel to fail. Rather, it is the fact that the undersurface of the panel is in tension as it repeatedly strikes against the upper surface of the tie so that tiny chips are broken away from the bottom surface of the panel, leading to eventual surface cracks and propagation of the cracks. Premature failure of a panel in such railway crossings is most likely to occur when the ties are unusually uneven. Although the tops of all the ties should be at the same height at the rail-attachment point, the top surfaces of the ties are often not at exactly the same heights except at the rail-attachment points. Also, some ties have manufacturers""logos or other writing in raised relief on their top surfaces. Concrete panels and concrete ties both have metal reinforcing bars included within the concrete, and these reinforcing bars can cause slight distortion of the surfaces of the concrete components. Further, due to the relatively large size of the panels, the underside surfaces of the panels may not be completely flat.
Variation in ties and concrete filler panels is taken into account when the panels are designed, and the amount of bending stress the panel might experience should not ordinarily cause the panel to fail. However, the panels still do fail, and in order to counter premature failure of the concrete panels, pads of rubber or rubberlike materials have been used atop the ties to distribute the loads of motor vehicle traffic more evenly. The presence of rubber tie pads between the ties and the panels distributes the forces caused by projecting irregularities on the tops of the ties, helps compensate for uneven ties, reduces the pressure applied to the bottom surfaces of the panel when it is in tension and protects the panel from repeated impact on the ties. Such a pad is disclosed in published Canadian patent application No. 2,281,110, and an article in the May 2000 issue of Mechanical Engineering. 
While pads may improve the longevity of the concrete panels, vibration caused by a train passing along the tracks at a grade crossing can cause the pads to migrate from their optimal position between the ties and the concrete filler panels, walking themselves out of position.
The pad disclosed in the Canadian application identified above includes end flaps to discourage movement of the tie pads. The pad disclosed in the Mechanical Engineering article uses a hollow cell to address this problem. Applicant believes that there are disadvantages to both these designs and has invented an improved tie pad.
The present invention provides an improved tie pad that resists movement with respect to its supporting tie. A tie pad according to the present invention has flanges that extend downwardly from the side margins of a main panel of the pad and upwardly projecting shoulders near the interconnection of the main panel with the flanges. The upwardly projecting shoulders provide frictional contact against the bottom surfaces of the concrete filler panels, and when pressed downward by the concrete filler panel, the shoulders push the flanges against the edges or sides of the tie, causing the pad to engage and grip the tie and preventing the pad from migrating from its proper position atop the tie.
The foregoing and other objectives, features, and advantages of the invention will be more readily understood upon consideration of the following detailed description of the invention, taken in conjunction with the accompanying drawings.